Guys,
I've decided to throw this problem out for some help or ideas.

My '98 vert is completely stock, top to bottom, no mods. Engine runs strong and everything seams to be working fine until I'm cruising along maintaining a constant speed at about 2,000 rpm and then it happens. The engine will miss causing the car to buck just a little, but it is really annoying. This car has a manual transmission which, I think, compounds the problem, or at least makes it seams worse. I've changed the air filter, plugs, plug wires, and fuel filter. I've only had this car 6 months and it's done it from the beginning. The car shows no codes, so I don't believe it is an electrical issue. Any help? Should my next step be to drain the gas tanks?
Thanks in advance,
Tony

 

Change plugs and wires.

 

Engine missing? Did you try looking under the hood? Sorry.. couldnt resist.

He said in the post that he changed the plugs and wires.


That is an odd problem. Does it only happen at 2k rpm? Does it smooth out after a certain rpm? Has it only been doing it for this current tank of gas?

 

Could be dirty fuel injectors--throw some fuel inj. cleaner in and taake it for a ride--sounds like a fuel problem--try it and let us know

 

Didn't notice he changed wires. I'd plug my laptop in and watch the misfires for each cylinder while I was driving-if it crosses a threshold on misfires it would set the MIL lamp though.

I'd still at least check the wires at the coils, takes 2 snaps to lock them and many people miss the second snap.

 

How do you know its an engine misfire?? What other indications do you see?? Does your Check Engine Light (CEL) "FLASH" during the problem??? That an indication of a misfire. During the problem while your driving, pull up the diagnostic routine and under the PCM you should see P-0300 engine misfire DTC. When you shut the engine off, that DTC gets cleared and you wont see it.

The secondary ignition (high voltage side) is NOT monitored by the diagnostic system. The reason you see the misfire DTC is that the Crank Shaft Position sensor detect the erratic firing of the cylinder/s and reports it. If you have a good scanner or something like EFI Live or HP Tuners, you can even nail it down to a specific cylinder/s

The reason I ask why you think its a misfire is, some people have other issues and report them as a misfire condition when it really wasnt.

Have you ever seen your gages act like they reset when the issue happens?????

There are plenty of things that can cause a misfire:

- Cracked Spark plug
- Damaged SP wire
- Spark Plug wire that isnt seated all the way
- Coil end of the wire that the metal connector is pushed too far down in the boot and makes poor connection on the coil tower. Seen that one too many times to count!!

There could also be a bad/loose connection at one of the coil connectors.

I have also seen the main engine wiring harness on the drivers side of the engine where it goes to the rear of the engine rub on a bracket and short out some wires. Seen that one three times!

Theres a Ground wire on the "BACK" of the drivers cylinder head. Thats the GROUND for the coils and fuel injectors. MAKE sure that the connection is tight and the wires are in good shape. The wires (there are two in one ground eyelet) are black with a white stripe.

Check all that out and let us know what you find.

Bill

 

Bill,

If the problem is only an occasional misfire the PCM may not set any codes or flash the MIL. My experience has been that the misfire has to be persistent for some period of time before the MIL flashes.

My gut feel, since this has done this since the OP got the car and has done the ignition work with no change, that the problem is fuel related (unless it's a chafing problem as you mentioned).

First step would be to see if there are any codes stored for the PCM. Then check the connections to the injectors (probably fine), then I'd probably get them cleaned/replaced.

Bottom line: transient problems like this can be insanely hard to pin down until they become persistent.

HTH, and have a good one,
Mike

 

I bought a good quality Auto Scanner to pull and read the DTC codes. Drove the car for 50 miles with no codes coming up. Checked all of the plugs and wires with no issues. I'm half way through a tank of gas with a bottle of injector cleaner. Is any one brand better than another? Wiring harnesses look good and ground wires tight. The miss is not steady, it is intermittent and most obvious at 2,000 rpm. I think it might be a fuel issue, since nothing is leading me to the ignition. I'll have the injectors looked at it tomorrow as I will be driving it a couple of thousand miles during Christmas week.
Many thanks,
Tony

 

fuel pump might be messing up. If all other checks out, try to get the fuel pump checked. Just my .02 Good Luck!

 

Tony,

Techron has the best reputation on this board, and I've seen it improve things. However, most agree that the best way to get them right is to remove them and take/send them to a shop that has the ability to really refresh the injectors.

It could possibly be a coil going bonkers as well; it's just so hard to figure out.

Good luck, and have a good one,
Mike

 

Good stuff for the price! I have in the past traced a defective injector down by listening to it with a mechanics stephescope. When the injector fires. it clicks. Compare all eight to each other and see if one or more sound different than the others.

If you can find some one with EFI Live, they can do a cylinder balance test for you. If one cylinder is not doing its fair share of the load, it will show up in that test.

BC


If you dont have or cant find a mechanics stephescope, make one out of a nail and 4 feet of vacuum line. Cut the head off of the nail and insert it into one end of the vacuum line. Put the nail on the part that you want to listen to and the other end in your ear. You will be amazed at how good it transmits noise from the touched part!

 

Just throwing this out there, I've read in the past that some code readers will miss codes. Have you used the DIC to check for codes?

 

My $.02. I think it's a fuel issue.
It seems if it were electronic, codes would be thrown.
If it were fuel pump at 2000 rpm, it may not run at 3-5k rpm, or it would be significantly worsen. A fuel pump pressure guage could answer this.
Are there any fuel leaks whatsoever? Sucking air anywhere? Has any part of the fuel system or intake recently been apart?
Does it seem like it could be one cylinder (one injecter), or low pressure to the entire fuel rail?

 

Pulled all injectors, three were very dirty. The car set up for a while before I bought it. Back together and problem seems to have gone away. Thanks a bunch. You guys gave me a lot of good places to look, and the car is in better shape than I thought. I put about 50 miles a week on it and that probably wasn't ample run time to clear the injectors even with injector cleaner.

 

No car likes to be parked and left alone. 50 miles a week is only about 2500 miles a year; surely you can do better than that!!!

Make a New Year's resolution to put at least 10,000 miles on you car in '09!

Have a good one,
Mike

 

While you are in there doing some maintenance,,might as well get some CRC MAF cleaner and clean the MAF an throttle body! That has perked up quite a few cars here on the forum!! Does not take long to do!!

 

cool!